This proposal from the California Center builds upon a five year research project, SEARCH for Diabetes in Youth, its standardized data collection effort, experienced investigator team, established case ascertainment infrastructure, and ethnically diverse population base. This is a common, integrated application from the six SEARCH clinical centers, which proposes to continue and expand the work performed by SEARCH in order to address the following specific research aims: AIM 1: Prospectively ascertain newly diagnosed (2006- 2009) incident cases age less than 20 years in order to estimate temporal trends in incidence of diabetes mellitus in youth; AIM 2: Conduct longitudinal follow-up of incident cases already recruited to SEARCH in 2002-2005 in order to document the evolution of newly diagnosed diabetes according to clinical and biochemical factors; AIM 3: Complete analyses initiated in the first five years of SEARCH and expand the scope of quality of care assessment to encompass more broadly defined concepts and measures of quality; AIM 4: Develop and validate simple and low-cost case definitions and classifications of diabetes types in youth that can be used for public health surveillance. The novelty of this proposal includes its comprehensive nature that brings together major and timely facets of childhood diabetes research: an epidemiologic study, unique in the United States, of temporal trends in the incidence of diabetes in youth; a pathophysiologic component addressing the natural history of diabetes in youth; a study of processes of care and quality of life; and a public health perspective on case classification of diabetes in youth. The strengths of the California Center are its large, diverse population; that most youth with diabetes receive health care from 1 of the 8 pediatric endocrinologists in the region; and the availability of a vast amount of electronic health data. Of the more than 770,000 youth less than 20 years, over half are Hispanic, African American, or Asian/Pacific Islander,which is representative of southern California. This research is critically important to public health. It will provide information about whether and how much diabetes incidence in the United States is increasing among youth of different backgrounds and how diabetes affects physical health, including complications, as well as data on the quality of care and the quality of life of youth with diabetes.